Headers for mowing crops having stalks so as to be harvested are used in combination with self-propelled, towed or attached forage harvesters for the total plant harvest, for example, for the harvest of silage corn. A commonly used type of such a header is described in EP 0 760 200A. The header of this publication includes a number of mower and intake drive assemblies arranged alongside each other for the mowing and transporting away of the plants along whose rear side the harvested crop is conducted to the center of the header. There it is conveyed to the rear into the intake channel of the forage harvester by means of discharge conveyors in the form of so-called slope conveyor drums which rotate about generally vertical axes which, however are inclined slightly in the forward direction, where the crop is compressed by rough pressing rolls and conducted to a chopper drum. The latter chops the harvested crop and conducts it to a blower that conveys the harvested crop from the forage harvester to a transport vehicle. The mower and intake drive assemblies and the discharge conveyors are connected with an output drive of the forage harvester over gearboxes with fixed speed ratios.
for a variation of the length of cut, the usual practice is to vary the rotational speed of the rough pressing rolls of the forage harvester, that can be performed by means of shifted gearboxes, adjustable hydraulic drives (for example, see WO 02/056672 A) or combined mechanical-hydraulic drives (WO 99/48353 A). At that point, the rotational speed of the chop[per drum remains approximately constant, so that the length of cut is inversely proportional to the rotational speed and the velocity of the rough pressing rolls.
At the present time, a trend towards longer lengths of cut can be observed. The longer lengths of cut require a relatively high velocity for the rough pressing rolls. In order to avoid problems in the transport during the transition of the plants from the discharge conveyor of the header to the rough pressing rolls of the forage harvester, caused by difference in speed, there is the possibility of also operating al driven elements of the header at higher rotational speeds. For this purpose, multi-speed shifted gearboxes are used. It has also been proposed that the front harvesting attachment be driven at a speed proportional to the rotational speed of the rough pressing rolls (WO 99/48353 A). The disadvantage in a variation of the rotational speeds of all driven elements of the header is seen in the fact that the rotational speeds of the mower and intake drive assemblies are also increased, although that speed increase does not bring about any improvement in the conveying of the harvested crop and hence is not necessary. It increases the power requirement of the drive and results in increased wear of the cutting knives and the braking arrangements of the header.
WO 02/056672 A describes a forage harvester with a header for mowing crops to be harvested, in which the slope conveyor drums are driven at a speed that is independent of the speed of the mower and intake drive assemblies. For this purpose, the rough pressing rolls and the slope conveyor drums are driven together by a first hydraulic motor while the remaining driven elements of the header are driven by a second hydraulic motor. Here the disadvantage is seen in the fact that two drive connections must be provided between the forage harvester and the header, that is, between the slope conveyor drums and the first hydraulic motor as well as between the remaining driven elements of the header and the second hydraulic motor. Thereby, the attachment and removal of the header to or from the forage harvester is rather time consuming. Furthermore, the efficiency of the hydraulic rives is relatively poor.
EP 1 055 359 A proposes that a transverse screw conveyor or transverse conveyor bands of a cutter head for a combine be driven hydraulically at an adjustable speed, while the beam of the cutter head is driven mechanically. The reel is driven hydraulically, at a fixed rotational speed. Here, too, a number of hydraulic drives with limited efficiency are provided.
The problem underlying the invention is seen in the need to make available a machine for harvesting crops having stalks that is improved over the aforementioned state of the art in which the velocity of the discharge conveyor is made to conform to the rotational speed of the rough pressing rolls of the forage harvester.